Single-phase motor with auxiliary coils selectively short-circuited by a solid state switch element

ABSTRACT

A single-phase, asynchronous motor of the split-pole type is provided with wound shading coils which are temporarily shortcircuited during starting operation by a controlled solid-state switching element, to which is applied a triggering signal derived from the current flowing through the stator winding.

llnite States Patent 1 Trouilhet 1 SINGLE-PHASE MOTOR WITH AUXILIARY ICOILS SELECTIVELY SHORT-CIRCUITED lBY A SOLID STATE SWITCH ELEMENT [75]Inventor: Maurice Marie Achille Trouilhet,

Lyon, France [73] Assignee: Calor, Lyon, France [22] Filed: Nov. 10,1971 [21] Appl. No.: 197,446

[30] Foreign Application Priority Data Nov. 30, 1970 France 7047330 [52]11.8. C1 318/221 E, 318/223, 318/227 [51] Int. Cl. 1102p 1/44 [58] Fieldof Search 318/220 R, 221 R,

[1 1 3,760,247 [451 Sept. 18, 1973 [56] References Cited UNITED STATESPATENTS 2,019,323 10/1935 Stark 318/223 X 3,573,579 4/1971 Lewus 318/221E 3,226,620 12/1965 Elliott et a1. 318/221 E 3,414,789 12/1968 Prouty318/221 E 2,341,482 2/1944 Stephan 318/223 Primary Examiner-Gene Z.Rubinson AttorneyFrancis T. Carr et a1.

[57] ABSTRACT A single-phase, asynchronous motor of the split-pole typeis provided with wound shading coils which are temporarilyshort-circuited during starting operation by a controlled solid-stateswitching element, to which is applied a triggering signal derived fromthe current flowing through the stator winding.

17 Claims, 7 Drawing Figures SINGLE-PHASE MOTOR WITH AUXILIARY COILSSELECTIVELY SIIORT-CIRCUITEI) BY A SOLID STATE SWITCH ELEMENT BACKGROUNDOF THE INVENTION DESCRIPTION OF THE PRIOR ART It is known that thestarting, in a desired direction, of a single-phase asynchronous motorcan be ensured only by artificial means whereby the alternating fieldpeculiar to such motors is changed, at least during the starting, into afield revolving in the desired direction. Such artificial meansgenerally involve the use of reactances associated with the motor, whicheither are cut off at the end of the starting or remain connected afterthe starting. In the first case, the motor must be provided withsuitable switch means, the control of which is often of the centrifugaltype and which complicate its structure and reduce its reliability inoperation. In the second case, the reactances considerably reduce themajor efficiency under normal operating conditions.

the starting of the motor, to which the auxiliary winding can thereforeefficiently contribute. On the contrary, when the motor rotatessubstantially at its nominal speed, the currentdrawn is considerablyreduced, so that the said solid-state element, which is kept non- Iconductive, cuts off the auxiliary winding circuit, and

the latter, although present, has no effect upon the operation of themotor, more particularly upon its efficiency.

According to other essential features of the invention, the saidauxiliary winding is formed of pairs of coils connected in series withat least one solid-state switch element, the number of turns and theimpedance of the said coils being advantageously so selected as toensure the supply of the ampere-turns required during the starting,without the maximum value of the current Among the known artificialmeans, one of those 7 which are used most often consists in providingthe motor with split stator-poles carrying an auxiliary winding orshading coil which is by-passed at least during the starting of themotor. As a result of induction, the said auxiliary winding creates analternating field shifted in time and space with respect to the inducingfield and which combines with the latter to create an elliptic fieldrevolving in the desired direction. The said auxiliary winding is mostoften constituted by lowimpedance rings surrounding a portion of eachinducing pole. A major drawback to this solution is that, although bcinghighly favourable to a good starting of the motor, it results in aconsiderable reduction of the motor efficiency.

SUMMARY OF THE INVENTION The present invention is therefore directed atproviding a single-phase asynchronous motor of the type comprising splitstator-poles carrying an auxiliary widing or shading coil which isby-passed at least during the starting of the motor, the latter beingprovided with arrangements capable of ensuring its starting in thedesired direction and with a sufficient torque, without howeverresulting in a reduction of its efficiency at normal speed.

To this end and according to an essential feature of the invention, thesaid auxiliary winding is by-passed by at least one controlledsolid-state switch element, to the control electrode of which issupplied a firing current which is substantially proportional to thecurrent drawn by the motor stator winding and which, during thestarting, reaches a sufficient value to fire the said solidstateelement, and then, at the end of the starting, drops to an insufficientvalue.

Thus, the auxiliary winding is effectively by-passed when the motordraws a strong current, i.e., when it produces a smallcounter-electromotive force and therefore rotates at a low speedcompared with the nominal or rated speed such conditions occur duringflowing therethrough exceeding that which the solidstate element canwithstand under steady operating conditions.

Moreover, a fuse is preferably connected in series with the said coilsand solid-state switch element, the rating of the said fuse being atmost equal to the maximum current which the solid-state element canwithstand under steady operating conditions.

An obvious advantage of the arrangements just mentioned isthat theyensure a perfect protection of the solid-state switch element againstany risk' of breakdown caused by overcurrent during the starting of themotor or resulting from an insulation fault in the auxiliary winding.

According to still other features of the invention, the firing currentsupplied to the control electrode of the solid-state switch element isprovided by a potentiometerwhich is either directly inserted in seriesin the supply circuit of the motor stator winding or supplied by acurrent transformer inserted in series in this same circuit.

In the second case, the auxiliary winding may be electrically insulatedfrom the supply circuit of the stator winding.

Obviously, such arrangements provide simple, sturd and adjustable meansof ensuring the required proportional relationship between the firingcurrent and the stator winding supply current, and therefore of settingat will the speed which the motor must reach in order that its startingauxiliary winding may be cut off.

The controlled solid-state switch element may be constituted by either abi-directional switch element, or TRIAC, or a uni-directional switchelement protected by a diode.

In the first case, a maximum motor starting torque is obtained, whereasin the second case the relative reduction of this torque is attended bya considerable reduction of the cost of the device. 4

In certain particular cases, the auxiliary winding of the motor may beby-passed by two unidirectional switch elements connected in parallel,poled in mutually opposite directions and each provided with a separatecontrol circuit.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of theinvention will appear more clearly from the following detaileddescription of several non-limitative examples of embodiment illustratedby the appended drawings wherein:

FIGS. 1 to 4 show the diagrams of four forms of embodiment of theinvention using bi-directional switch elements or TRIAC and I FIGS. 5 to7 show the diagrams of other forms of embodiment of the invention usingunidirectional switch elements.

DESCRIPTION OF THE PREFERRED EMBODIMENT The bipolar motor, the diagramof which is shown in FIG. 1, comprises a short-circuited rotor Rrotating in the field of a stator winding S1-S2 formed of twosymmetrical half-windings connected in series to the termi-.

nals of a single-phase a.c. source.

The inducing poles carrying respectively the stator windings 81-82 aresplit and partially encircled by the symmetrical portions B1, B2 of astarting auxiliary winding, which are connected in series so as to forma closed circuit with a fuse F and a bi-directional semiconductor switchelement or TRIAC Tr. The control electrode or firing gate G and thecorresponding cathode of the latter are respectively connected to theslider and to one of the terminals of a potentiometer P inserted inseries in the supply circuit of the stator winding Sl-S2.

Thus, when a current I flows through the stator winding 81-82, thecontrol electrode G of the bi-directional need, by a resistance-capacitycircuit connected in parallel as shown in dashed lines. 7

The device of FIG. 1 is perfectly suitable where the voltage range isnot too high and in case the auxiliary winding 81-82 is properlyelectrically insulated with respect to the stator. Under the samevoltage conditions, but in case of a less reliable insulation of theauxiliary winding Bl-B2, the device of FIG. 2 may be advantageouslyused.

In this device, the firing gate G of the bi-directional switch elementTr is fed by a potentiometer P which is itself supplied by the secondarywinding of a current transformer J, the primary winding of which isconnected in series in the supply circuit of the stator winding Sl-S2.Thus, the circuit of the auxiliary winding 81-82 and the control circuitof the switch element Tr are perfectly insulated from the stator winding81-82.

In case of higher voltage variation ranges, the devices of FIGS. 3 and 4are used advantageously.

The device of FIG. 3 is similar to that of FIG. 1, except that thefiring gate G of the bi-directional switch element Tr comprises twobiasing circuits, each of switch element Tr is supplied with aproportional current 1', the coefficient of proportionality dependingupon the position of the slider of the potentiometer P. The saidposition is selected so that the current i may be sufficient to tire theswitch element Tr during the starting stage while the motor rotating atlow speed produces a small counter-electromotive force and thereforedraws a strong current I the position of the slider of the potentiometerP is also selected so that at the end of the starting the current iproportional to the nominal value of the current drawn by the motor beinsufficient to fire the bi-directional switch element Tr. Thus, thelatter is selectively driven into conduction or kept non-conductiveaccording to whether the motor is being started or has reached a givenspeed approximating to its nominal speed.

The coils Bl-B2 of the startingauxiliary winding are advantageouslyconstituted by several wire turns, so as to be capable of producing themagneto-motive force required for a good starting of the motor, takinginto account the structure of the rotor R, without the current passingthrough the said coils exceeding the value permitted by the switchelement Tr under steady operating conditions. Otherwise stated, thecoils Bl-B2 must be capable of supplying the required number ofampere-turns and their impedance must be high enough to limit thestrength of the current flowing therethrough under any circumstances toa value compatible with thecharacteristics of the switch element Tr.Indeed, owing to the time lag of the fuse F on overload, it cannotensure by itself a reliable protection of the switch element Tr, forinstance in case of stoppage of the motor caused by an excessiveresisting moment, the said stoppage causing a strong current I to bedrawn and therefore a sufficient current i to be supplied to the firinggate G of the switch element Tr to drive the latter into conduction. Anadditional protection of the bidirectional switch element with respectto abrupt voltage and current variations may be ensured, in case ofwhich is formed of a diode D1, D2 connected to the slider of apotentiometer P1, P2, the said diodes being poled in mutually oppositedirections, whereas the said potentiometers are connected in parallelwith a fixed resistance P", mounted in series, in the same manner as thepotentiometer P in the supply circuit of the stator winding 81-82.

I The device of FIG. 4 includes the same modification with respect tothe device of FIG. 2, the firing gate G of the switch element Tr beingconnected by diodes D1, D2 to the sliders of the potentiometers Pl, P'2supplied in parallel from the secondary winding of a current transformerJ, the primary winding of which is connected in series with the statorwinding 81-82.

The devices of FIGS. 5 and 6 correspond respectively to those shown inFIGS. 1 and 2, but differ therefrom essentially in that thebi-directional semi-conductor switch element Tr is replaced by auni-directional semiconductor switch element Th whose firing gate G isprotected by a diode D. With the indicated coupling and wiringdirections, the unidirectional switch element Th is therefore driveninto conduction during only the half periods 11 of the supply current ofthe stator winding 81-82. This, of course, results in a nonuniformstarting torque whose value is half that of the previous one, owing tothe fact that the auxiliary winding 81-82 is closed only during the halfperiods in a given direction of the alternating supply current thisdrawback may however be acceptable under certain conditions of use,considering that the cost of a unidirectional switch element Th is muchlower than that of a bi-directional switch element or TRIAC Tr.

The device of FIG. 7 is applicable to all cases where maximum startingtorque is necessary but two separate control circuits are required.

This device comprises two unidirectional switch elements Th1, Th2connected in parallel, poled in mutually opposite directions and whoserespective control electrodes G1, G2 are connected, through the mediumof diodes D1, D2 poled in one and the same direction, to the sliders ofpotentiometers P'l, P'2 supplied respectively from two separatesecondary windings of a current transformer J' whose primary winding isconnected in series with the stator winding 81-82. In the indicatedwiring and coupling directions, the switch elements Th1 and Th2 arealternately driven into con duction during the half periods 11 and [2 ofthe supply current of the stator widing Sl-S2.

From the examples of embodiment described and illustrated, it appearsthat the invention enables a singlephase asynchronous motor to beimparted the same starting torque as that of a motor of the same typeequipped with conventional starting rings, while at the same timeensuring a much higher efficiency. The consequential advantages offeredby the invention consist in that the auxiliary winding may be made fromthin wire, thus considerably reducing its overall dimensions, and thatits switching is obtained by means of a controlled solid-state switchelement of higher reliability and smaller overall dimensions than thoseof a conventional electromechanical relay. As a result, the inventionenables the dimensions of a motor to be reduced, as compared with thoseof a motor of the same power provided with low impedance rings, and thecost of the motor to be reduced owing to the simplicity of the devicesused, which besides enable the switching threshold to be adjusted atwill. in addition, the said devices occupy less space and are lessexpensive than those using a phase-shifting capacitor.

Of course, the invention is by no means limited to the forms ofembodiment described and illustrated which have been given by way ofexample only. In particular, it comprises all the means constitutingtechnical equivalents to the means described as well as theircombinations, should the latter be carried out according to the spiritof the invention.

What is claimed is:

1. A single-phase asynchronous motor, comprising:

a stator provided with a plurality of split poles, each of which carriesa respective field-inducing main winding and is partially encircled by arespective flux-shading auxiliary winding consisting of a plurality ofturns of a single wire;

a short-circuited rotor operatively mounted for rotation in said stator;v power circuit means operatively connecting said main windings to theterminals of an ac. singlephase power supply; starting circuit meansconnecting serially said auxiliary windings in closed loop with at leastone solidstate switch element having a control electrode and adapted toselectively short-circuit said serially connected auxiliary windingsupon application to said control electrode of a firing current exceedinga predetermined value; and control circuit means including an adjustablecurrent divider operatively connected to said switch element and to saidpower circuit means for supplying to said control electrode of saidswitch element a firing current substantially proportional to thecurrent in said power circuit means, said current divider being set sothat said firing current exceeds said predetermined value by thestarting of said motor and then drops below said value at the end ofsaid starting.

2. A motor according to claim 1, wherein the impedance of said startingcircuit means and the total number of turns of said auxiliary windingsallow for induction therein of a current sufficient to provide theampereturns required by the, starting of said motor but prevent themaximum value of the current induced through said starting circuit meansfrom exceeding that which said switch element can withstand under steadyoperating conditions.

3. A motor according to claim 2, wherein said starting circuit meansadditionally includes a fuse, .whose rating is at most equal to themaximum value of the current which said switch element can withstandunder steady operating conditions.

4. A motor according to claim 1, wherein said starting circuit meansincludes a resistance-capacity circuit by-passing said switch elementand operative to clamp abrupt voltage and current variations.

5. A motor according to claim 1, wherein said starting switch element isa bi-directional semi-conductor switch or TRIAC, and wherein saidcurrent divider comprises a single potentiometer, to the slider of whichsaid control electrode of said switch element is directly connected.

6. A motor according to claim 5, wherein said potentiometer is includedin series in said power circuit means.

7. A motor according to claim 5, wherein said potentiometer is connectedin parallel to a resistor included in series in said power circuitmeans.

8. A motor according to claim 5, wherein said potentiometer is fed bythe secondary winding of a current transformer, the primary winding ofwhich is included in series in said power circuit means.

9. A motor according to claim 1, wherein said switch element is abi-directional semi-conductor switch or TRIAC, and wherein said currentdivider comprises a double potentiometer, to the sliders of which saidcontrol electrode of said switch element is connected through theintermediary of respective diodes poled in opposite directions.

10. A motor according to claim 9, wherein said potentiometer is includedin series in said power circuit means.

11. A motor according to claim 9, wherein said potentiometer isconnected in parallel to a resistor included in series in saidpowercircuit.

12. A motor according to claim 9, wherein said potentiometer is fed bythe secondary winding of a current transformer, the primary winding ofwhich is included in series in said power circuit means.

13. A motor according to claim 1, wherein said switch element is auni-directional semi-conductor switch or thyristor, and wherein saidcurrent divider comprises a single potentiometer, to the slider of whichsaid control electrode of said control element is connected through theintermediary of a diode.

14. A motor according to claim 13, wherein said potentiometer isincluded in series in said power circuit means.

15. A motor according to claim 13, wherein said potentiometer isconnected in parallel to a resistor included in series in said powercircuit means.

16. A motor according to claim 13, wherein said potentiometer is fed bythe secondary winding of a current transformer, whose primary winding isincluded in series in said power circuit means.

17. A motor according to claim 11, wherein said switch element consistsof a pair of uni-directional semi-conductors switches or thyristorsconnected in parallel and poled in mutually opposite directions, andwherein said current divider comprises a pair of potentiometersrespectively fed by separate secondary windings of a current transformerwhose primary is included in series in said power circuit means, saidcontrol electrode of said switch elements being respectively connectedto the sliders of said potentiometers through the intermediary ofrespective diodes.

k *0 k i 3

1. A single-phase asynchronous motor, comprising: a stator provided witha pluRality of split poles, each of which carries a respectivefield-inducing main winding and is partially encircled by a respectiveflux-shading auxiliary winding consisting of a plurality of turns of asingle wire; a short-circuited rotor operatively mounted for rotation insaid stator; power circuit means operatively connecting said mainwindings to the terminals of an a.c. single-phase power supply; startingcircuit means connecting serially said auxiliary windings in closed loopwith at least one solid-state switch element having a control electrodeand adapted to selectively short-circuit said serially connectedauxiliary windings upon application to said control electrode of afiring current exceeding a predetermined value; and control circuitmeans including an adjustable current divider operatively connected tosaid switch element and to said power circuit means for supplying tosaid control electrode of said switch element a firing currentsubstantially proportional to the current in said power circuit means,said current divider being set so that said firing current exceeds saidpredetermined value by the starting of said motor and then drops belowsaid value at the end of said starting.
 2. A motor according to claim 1,wherein the impedance of said starting circuit means and the totalnumber of turns of said auxiliary windings allow for induction thereinof a current sufficient to provide the ampere-turns required by thestarting of said motor but prevent the maximum value of the currentinduced through said starting circuit means from exceeding that whichsaid switch element can withstand under steady operating conditions. 3.A motor according to claim 2, wherein said starting circuit meansadditionally includes a fuse, whose rating is at most equal to themaximum value of the current which said switch element can withstandunder steady operating conditions.
 4. A motor according to claim 1,wherein said starting circuit means includes a resistance-capacitycircuit by-passing said switch element and operative to clamp abruptvoltage and current variations.
 5. A motor according to claim 1, whereinsaid starting switch element is a bi-directional semi-conductor switchor TRIAC, and wherein said current divider comprises a singlepotentiometer, to the slider of which said control electrode of saidswitch element is directly connected.
 6. A motor according to claim 5,wherein said potentiometer is included in series in said power circuitmeans.
 7. A motor according to claim 5, wherein said potentiometer isconnected in parallel to a resistor included in series in said powercircuit means.
 8. A motor according to claim 5, wherein saidpotentiometer is fed by the secondary winding of a current transformer,the primary winding of which is included in series in said power circuitmeans.
 9. A motor according to claim 1, wherein said switch element is abi-directional semi-conductor switch or TRIAC, and wherein said currentdivider comprises a double potentiometer, to the sliders of which saidcontrol electrode of said switch element is connected through theintermediary of respective diodes poled in opposite directions.
 10. Amotor according to claim 9, wherein said potentiometer is included inseries in said power circuit means.
 11. A motor according to claim 9,wherein said potentiometer is connected in parallel to a resistorincluded in series in said power circuit.
 12. A motor according to claim9, wherein said potentiometer is fed by the secondary winding of acurrent transformer, the primary winding of which is included in seriesin said power circuit means.
 13. A motor according to claim 1, whereinsaid switch element is a uni-directional semi-conductor switch orthyristor, and wherein said current divider comprises a singlepotentiometer, to the slider of which said control electrode of saidcontrol element is connected through the intermediary of a diode.
 14. Amotor according to claim 13, wherein said poTentiometer is included inseries in said power circuit means.
 15. A motor according to claim 13,wherein said potentiometer is connected in parallel to a resistorincluded in series in said power circuit means.
 16. A motor according toclaim 13, wherein said potentiometer is fed by the secondary winding ofa current transformer, whose primary winding is included in series insaid power circuit means.
 17. A motor according to claim 1, wherein saidswitch element consists of a pair of uni-directional semi-conductorsswitches or thyristors connected in parallel and poled in mutuallyopposite directions, and wherein said current divider comprises a pairof potentiometers respectively fed by separate secondary windings of acurrent transformer whose primary is included in series in said powercircuit means, said control electrode of said switch elements beingrespectively connected to the sliders of said potentiometers through theintermediary of respective diodes.